The objectives of our research program concern the study of control of macromolecular synthesis and function. In particular, we have been studying the ways in which bacterial viruses interact with and affect their host, in our case, Escherichia coli. Our work concerns two main areas: (1) DNA restrictions and modification, and (2) bacterial DNA synthesis. (1) DNA restriction and modification. Bacteriophage lambda has a gene which allows unmodified lambda DNA to escape from restriction by the E. coli K restriction by the E. coli K restriction system. We are attempting to determine the mechanism of this escape (a) in vivo, by seeing whether other restriction systems (e.g., Pl, E. coli B) are affected and (b) in vitro, by seeing whether induced lambda extracts inhibit restriction enzyme binding to DNA or cleavage of DNA, or perhaps stimulate modification. (2) Bacterial DNA synthesis. We have been studying behavior of bacterial strains with a severe deficiency in E. coli DNA polymerase I. Under certain growth conditions (especially in rich medium), these strains grow poorly. We are investigating the reason for this defect by measuring DNA synthesis and repair under a variety of growth conditions to see whether DNA polymerase I is involved in bacterial DNA replication. In addition, we are isolating new mutants lacking this enzyme by a selective technique.